1. Field of the Invention
This invention relates to a method for coupling lightguides to fiber optic transmission lines.
2. Description of the Related Art
In the electro-optic or photonics industry, it is frequently necessary to couple lightguides with fiber optic transmission lines, e.g., when coupling an optical component on a circuit board to a light pipe. A major problem when coupling lightguides to fiber optic transmission lines is that typically lightguides have a high “refractive index difference” (Δn) percentage between the core and the cladding as compared to the Δn of fiber optic transmission lines. A typical on-chip or on-circuit board planar lightguide has a Δn of 4-5%, while a typical fiber optic transmission line has a Δn of approximately 0.5-2%. This significant drop of Δn between the lightguide and the transmission line causes problem, e.g., reflection resulting in a reduction in the amount of light that can be transmitted. To solve this problem, optical coupling techniques have been used to ease the transition from this low-to-high or high-to-low Δn's, for example, lenses are used to focus (or spread) the light, making the transition more gradual. While functioning adequately, prior art techniques are custom solutions that are costly and that take up significant space on a circuit board or other location where space is at a premium.